Two-stroke internal-combustion engine



u J1-me 25, 1929. F. ROCHEFORT .A 1,718.879

TWO-STROKE INTERNAL COMBUSTION ENGNE Filed Sept. 22, 1925 2 Sheets-.Sheet l Figi.

III IH au en Ill June 25, 1929. F, RO'CHEFORT 1,718,879

TWOSTROKE vINIIilRImL COMBUSTION ENGINE Filed Sept. 22, 1925 2 Sheets-Sheat 2 Patented June 25, 1929,

UNITED STATES FR-ANQOIS ROCHEFORT, 01T' PARIS, FRANCE.

TWG-STROKE INTERNAL-CMBUSTION ENGINE.`

Application filed September 1925, Serial No. 57,917, and in France September 25, 1924n Two-stroke engines without poppet valves are known, having total or partial dist1fibu tion by reciprocating oi rotating slidcvalves or which combine those two systems toget-her.

ln certain motors with total distribution the slide valve forms the inner part ot the enginescylinder and oit the scavenging pump cylinder, the pistons moving in this part of the cylinders.

ln this arrangen'ient, the slide valve must have the same length and diameter as the cylinders, which renders it heavy. Since, further, it iforms the werking chamber tor the combustion. gases, it must withstand the high pressure and temperature oit these gases.

rlhis kind of distribution or timing does not allow high speeds of rotation to be obtained, by reason oit the inertia ol the slidevalve; it renders lubrication ditlicult because ot the temperature ot the walls, and, by not allowing very accurate adjustment et the distribution, it limits the global efficiency of the motor to a low value.

ln other motors, the valve is rotary and carried outside the working cylinder, at the height oil the ports for the entry of scavenging air. Although the temperature of the walls ot' the slide valve may be lessin this arrangement than in that which has just been mentioned, it is still too high. Moreover, this arrangen'ient, being less gas-tight, allows the passage between its wall and that oit the cyliinler in which it rotates, ot gases which have expanded but are still at a high tempera ture, which has for el'ect to cause the deposit upon these walls, of carbon residues resulting from the incomplete combustion. of the gases, these residues rendering the working less certain by giving rise to the dangers of the slide valve seizing in its seat. The lack oit gasstigl'itness ot the arrangement causes also losses oit clliciency `in the scavenging pump. The arrangement adopted docs not permit of accurate and precise adjustments ot the opening and closing points ot the ports ttor the admission and the discharge of the air to and from the scavening pump, and the throttling of the air or gases passing through the ports is increased, from the very fact that the circumferential speed of the rotary valve is constant, it' itv be wished to retain reasonable dimensions for this valve. Lastly, ports having dill'erent functions are in the saine plane, so that it is not possible to avoid or to counterbalance the side thrusts on the part el the burnt gases still under pressure when the working scavenging ports.

There exist, it true, engines in which the distribution is ensured for each working cylinder by two or three separate reciprocating having indcjliendent functions and movements. This arrangement has the advantage of permitting accurate adjustments but it enormously complicates the operating clevices, the piping, and the joints, and renders laborious the construct-ion and maintenance ol such an engine which it is dilficult to build conveniently.

The presentinvention has for its object an :internal combustion engine working on the two-stroke cycle preferably with direc-t .injection of the fuel into the Working cylinder.

The construction ot this engine enables to be suitably ensured (l) The correct timing tor the suction and the delivery ol air into and from the scavenging ump. j

(2) The precise adjustment of the moment of introduction of the -scavening air into the engine cylinder, after complete expansion of the burnt gases. j

(3) The perfect filling of the cylinder volume with pure air and, for certain uses, the supercharging of the Working cylinder by a retarded closing of the inlet ports1 Well atter the closing of the exhaust ports for the escape of the burnt gases.

In this way the passive resistance are reduced to the minimum, complete evacuation oil? the burnt gases is effected, by a more efficient scavenging, and a higher specific cficiency of the engine is obtained.

The engine according to the invention is piston uncovers the slide valves or by slide and poppet valves characterized by the use for each Working cylinder of a single cylindrical distributing piston Valve itted with piston rings, and having rectilinear reciprocating movement in a small cylinder placed parallel With the working cylinder and communicating there` wit-h only by the ports for the admission of scavening air, formed in the base, in order that the walls of the distributor slide valve and of its cylinder shall be never in contact with gases of high pressure and temperature.

This distributor slide valve performs the samenumber of strokes as the working piston, its driving crank revolving at the same speed asthe engine shaft, but it is timed to follow after the driving crank shaft in order to obtain a. better adjustment of the distribution.

In case it is employed in slow running engines, this slide valve may be provided interiorly with an obturator diaphragm which Vobviates a loss of elliciency occasioned by the resistance which would result from the setting Aup of currents in the opposite direction at the opening of the pump delivery outlets While the pressure of the air contained in the scavenging collector is still higher than that which exists in the air pump at the commencement of its delivery stroke. Y

This obturatorl becomes unnecessary when the engine has to run at high speeds, the inx vertia of the air being then sufficient to overcome the phenomenon indicated.

The cylinder of the distributor slide valve is provided with two annular chambers, completely surrounding the distribution ports, in

4recting device being interposed :t'or that purpose between the slide valve and the connectrod which operates it.

e arrangement of the annular chambers around the portsVV enables large sectional areas to be provided for the passage of the scavenging air, whilst vrequiring a very restricted Y -.stroke for theslide valve which can be of very small dimensions.

In the case of aviation motors, there is providedY upon the control mechanism for the Slide-valves, between the driven gear wheel andthe timing shaft, an arrangement for a1- tering the angular setting of the distributor slide lvalves relativel` to the engine shaft, in

order to vary the vo ume of air delivered by the scavenging pump and to regulate the filllingofthe working. cylinder volume for the purpose of maintaining the compression more or less constant, at the various altitudes at which the engine is requiredA to work, the characteristics of the air pump being naturally selected with a view to the rational utilization'of this kind of adjustment.

HThe actuation of the slide valve is positive "in bothedirections and is very easily a plied to thmconsitruction of directly reversib e motors `(for-"example for marine engine sets) by meansof the employment of an angular setting adjustment similar to that which has been indicated above. The actuation can be effected by any one of the known means, such ample an engine constructed according to the invention.

Figure l is a section through a vertical plane perpendicular to the crank shaft.

Figures 2 to l0 reproduce Figure 1 diagrammatically on a smaller scale and are intended to illustrate the various phases in the working of the engine.

As shown on the drawing (Figure 1), the motor comprises a cylinder C-C in which there reciprocates a piston of two corresponding diameters l) l1 of one of the known types provided with a deflector el at its top.

Upon the side oi the engine cylinder C :ind at its lower part is arranged a small cylinder C2 in which the distributor slide-valve I2 reciprocates, being actua-ted by a small connecting rod b and a small timing or distribution c 'ankshaft m, driven at a speed equal to that of the engine shaft M either by direct geuring or by a silent chain, as shown in Figure l.

A chamber A is in consta-nt communication with the atmosphere by means of :i ganze or screen intended to prevent foreign matter from entering the air pump. The latter is formed by the lower large-bore cylinder C" and the corresponding piston l". lorts L allow the cylinder C1 to communicate either with the atmosphere through the chamber A or with the collector c, according to the position of the bottom end of the slide l2 and ot the ports L1 spaced around the cireum't'erem'c of the wall of the distributor slide; porls L2 spaced around the wall of the small cylinder C2 eil'ect communication of the latter with the working cylinder C by the intermediary of the ports Ls for the admission of scavenging air.

Other ports L4 formed in the wall of the working cylinder C allow the release and cxhaust of the burnt gases into the atmosphere at the end of the stroke of the working piston P.

This exhaust takes place into an expansion chamber, energetically cooled, and afforded by the exhaust manifold A device for injecting and atomizing the fuel is arranged at J at I is arranged an elec4 tric i nition device to ensure immediate starling rom cold. An igniting bulb plate, 'l` raised to a high temperature by the combustion of the gases, provides the normal ignition. It may even permit rapid starting by causing ignition by external heat if the .small bulb situated in the centre of the plate be lllU heated. This bulb can be brought to a dull red heat in a very short time either by the aid of a cartridge of suitable material or by usmg a small blow pipe mounted upon the engine for that purpose.

The distribution shaft m has its crank otl`- set by an angle of about 100O rearwards in relation to the crank o1 the engine shaft M and to the direction el. rota-tion of this latter, in order to obtain port opening and closing l points as correct as in the case ot imlependently operated poppet valves and to otter the largest passage areas for the scavenging air at the moment of maximum speed of the piston P1 of the scavenging pump as well as during the periods of gas scavenging and et cylinder-charging after the closing of the exhaust ports L4.

The working of this engine is as follows z- The engine being started in the direction et the arrow in Figure 1, the piston commences its working stroke (period et expansion a't'ter ignition); it has then passed the top dead centre, the crank pin of the engine shaft has passed the vertical axis by some 'lcw degrees, the slide valve P2 justcloses the ports L communicating lwith the interior ot the cylinder pump C1, thatis to say this closure takes place with a certain lag in order to allow the pressure ot' the air enclosed in the clearance or neutral space of the scavenging pump, to balance the pressure obtaining in the scavenging air collector c, which has just been charged with pure air at a slight pressure. rPhe slidevalve P2 rises rapidly, by reason of the setting of the cranks, while the piston P1 passes through a small fraction of its downward stroke, creating a slight i'all et pressure above it.

The slide P2 still rising (Figure Q) its base uncovers the ports L, and a current ot' cold air caused by the tall of pressure created in the cylinder C1, `passes in rapidly through the chamber A and the ports L.

The piston P1 continues to descend. with increasing speed while the slide, still rising, reaches the end of its stroke, wholly uncovering the ports L in order to facilitate the filling of the air pump (Figure The Working stroke continuing, the engine piston P next uncovers the top of the ports L3 for the admission of scavenging air but, at this moment, the slide valve P2 closes these ports and cuts off anycommunication with the collector e, leakage being prevented by rings above and below the ports L2 ot the small cylinder C2.

The burnt gases, having expanded in the engine cylinder C, penetrate `for a very short time into the space comprised between the ports and the annular chamber which surrounds the small cylinder C2; there is no lateral thrust upon the slide valve, because the pressure of the gases acts uniformly around the whole circumference.

The expansion stroke continues until the Working pistonP uncovers the exhaust ports L4; at this moment, the distributor slide valve P2 has passed the top of its upward stroke and commences to desc-end. The working piston completes the opening of the exhaust ports LA17 (Figure 5), and the burnt expand rapidly into the exhaust manifold lil comuninicating with the atmosphere. lVhen the burnt gases are completely expanded, there is a contraction of the gases, and a certain tall of pressure is created in the cylinder C.' At this instant (see Figure (S), the distributor slide valve which is well upon .its (ilescendin stroke, suddenly uncovers the ports L2 ot the Fsmall cylinder C2; the air compressed in the collector' c on the preceding stroke, expands and rushes into the engine cylinder, being drawn thereinto by the tall ot pressure due to the exhaust. This air is directed towards the top e o'f the cylinder head by the deliector l formed upon the top ot' the working piston P and drives the burnt gases `betere it The momentum of the scavenging air is utilized to its maximum by means oi a careful adjustment et the point of opening ot the ports L, which adjustment causes the expansion, of the compressed air ttor scavenging to coincide with a pronounced 'fall et pressure in the exhaust. There is thus obtained a coinplete evacuation of the inert gases whilst limiting the duration oi' the period oif scavenging (the exhaust pipe being determined and designed to that end), which constitutes a great advantage for high speed engines.

As the main piston P1- approaches the end ot its stroke, the air-pump has just tinished its period tor admitting cold air; the slide valve commence to close the ports L (Figure 6). Continuing its stroke, the engine piston reaches the bottom centre, but the slide valve closes the ports L with a slight lag; the supply into the pump cylinder `C continues through the openings 0 uncovered at the end of the stroke by the piston PlL and communicating with the atn'iosphere by the extremities of a collector A1 formed in the crank chamber of the engine and at the upper part t-hereo'l.

"llhese openings 0 providetor a delay or la g in the closing ot the admission ot air ttor the scavenging pump, in order to have a perfectly full charge (Figure 7) The working cylinder is at this moment in the very midst ot scavenging the burnt gases. Continuing its stroke, the working piston passes the lower dead centre and commences to rise; the openings 0 are covered again by the piston P1, the distributor sli-de valve having already closed the ports L.

rPhe piston P1 in its ascending stroke slight ly compresses the air admitted into its cylinder C1, whilst the slide valve still descending brings the ports L1 termed in its periphery (Fig. 8) into position opposite the ports L of the small cylinder C2 and of the air pump which is then at the beginning of its stroke for delivering into the collector 0 in which the scavenging air is to be stored.

In the case of a slow running engine, the ports L1 are separated from the upper opening ofthe piston valve P2 by adisc valve D, the lift of which is limited by a stop piece Vor hea-d D1 (these two devices are shown in broken lines in Fig. l). The -disc valve D willbe lifted as soon asthe pressure of air in Clis greater than that which exists in the collector, the latter thus continuing to be supplied. The inertia of this valve facilitates its opening as well as its closing.

The working cylinder C is represented in Fig. 8 in full Yscavenging operation, the engine piston being then on its upward stroke; when it closes the exhaust ports L4, the scavenging phase is ended, the motor piston reaching the position indicated in Fig. 9.

The ports L3 intended for the admission of air to the working cylinder remain still o en for a certain time in order to allow the cy inder C to b e properly charged; the airvpump is during this time in full delivery and contributes to the filling of the working cylinder by u feeding lthe collector c. y

The engine piston, continuing its upward stroke, closes the admissionports L3 when the pressure of air contained in the cylinder C is almost in equilibrium with that which exists in the collector c (Fig. l0).

The effective compression thereupon commences in the engine cylinder C whilst the collector -0 becomes charged with fresh air at low pressure, delivered by the air pump, in' suflicient quantity for the next scavenging operation.

' Before the working piston reaches the end of the compression stroke, the injectingatomizing device fitted at J introduces the charge of fuel which is finely atomized and diffused in the vpure air compressed by the working piston. In these conditions, mixture is rapidly effected, ignition occurring r`at the end of the stroke and creating a rapid rise'of pressure of the gases which afterwards expand doing useful work.

The piston P after passing the top dead centre, commences its working or expansion stroke; the distributor slide valve P2 rises and closes the. ports L at the end of the delivering stroke of the air pump and the cycle recommences as has been described.

It will thus be seen that in this engine (l) The burnt gases are completely expanded before the introduction of the scavenging air in such a way as better yto utilize the momentum of the compressed air with complete by reason of the intrmluction of a volume of fresh air greater than the total capacity of the working cylinder, that is to say than the volume swept by the working piston increased by the clearance space of the combustion chamber.

(3) Perfectly full charging of the working cylinder with fresh air and in certain cases supercharging are obtained by the conjunctive action of. a considerable delay or lag in the closing of the inlet ports Ln and of those of the air pump which delivers into the scavenging air collector during the closing ofthese ports,

(4) Scavenging is effected by fresh and cold air, which is not saturated with vapours of the lubricating oil contained in the crank chamber, because this air does not pass into the latter.

rIhe fuel being introduced into the engine cylinder only well after the closing of the ports, which is effected in the middle of the compression stroke, there is no loss of fuel through these ports. It is however to be understood that the application of the inven ytion is not limited to engine having direct injection of fuel only.

What I claim is I In an internal combustion engine including a cylinder having an inlet port, a piston working in said cylinder, an air supply chamber7 and a valve for controlling the sup )ly of air from said chamber to the c lin er, in combination with a iston valve or controlling the supply of c large through the inlet port, the said piston valve moving for a proximatel a half-stroke with respect to t le piston andy attaining its maximum linear speed at the period of admission of air from said air supply chamber to the cylinder.

In'testimony whereof I have signed my name to this speelflcatlon.

FRANCOIS ROCHEFORT. 

